The invention relates to the synthesis of amido acid phenyl esters by single-stage reaction of amidocarboxylic acids with inorganic acid halides and a phenol derivative.
Amido acid phenyl esters are used as bleach activators in detergents and cleaners. They permit a bleaching action at temperatures below 60.degree. C. by reacting with a source of hydrogen peroxide, in most cases perborate or percarbonates, to liberate an organic peroxy acid.
The patent literature describes various processes for the syntheses of these bleach activators.
For example, U.S. Pat. No. 5,523,434 describes the preparation of amido acid phenyl esters from amidocarboxylic acids and phenolsulfonates by a two-stage process: in the first stage, an amidocarboxylic acid chloride is synthesized by reaction of the amidocarboxylic acid with inorganic acid chlorides, and in a second step, the amidocarboxylic acid chloride is reacted with a phenolsulfonate in a water/diethyl ether mixture. Problems associated with the industrial applicability of this process are the use of diethyl ether as solvent, the low storage stability of the amidocarboxylic acid chloride and the use of large excesses of inorganic acid chloride.
U.S. Pat. No. 5,466,840 likewise describes a multistage process for the synthesis of amido acid phenyl ester sulfonates. It involves reacting the alkali metal salt of a 4-hydroxybenzenesulfonic acid with a C.sub.2 -C.sub.4 -carboxylic anhydride to give the alkali metal salt of a 4-acyloxybenzenesulfonic acid. In a second stage, the latter is converted to the amido acid phenyl ester sulfonate by addition of 1-oxyalkanoylaminocarboxylic acid in the presence of a transesterification catalyst at from 150 to 250.degree. C. over the course of from 0.5 to 10 hours. A disadvantage of both synthesis routes is that they require two or more reaction stages with intermediates which in some cases are not very stable. The formation of by-products, yield losses and laborious purification processes for the products increase the cost of the preparation of this class of compound, which is used as bleach activators in detergents and cleaners.
The process according to WO 96/39378 involves introducing amidocarboxylic acid and a phenol derivative into sulfolane, dropwise addition of a carboxylic anydride, for example acetic anhydride, and achieving conversion to amido acid phenyl ester sulfonates by heating to about 170.degree. C. over the course of from 0.5 to 10 hours depending on the starting compound.
Unsatisfactory aspects are the very high expenditure of energy while carrying out the reaction, reduced yields, heavily contaminated products and the very laborious and costly removal of the high-boiling solvent. The object was therefore to find an improved procedure for the preparation of amido acid phenyl ester sulfonates.